It is known that mitomycin C, bleomycin, adriamycin or the like compound derived from a microbial metabolite shows cytotoxic activity for human cancer cells, and these compounds are conventionally used as antitumor agents in the clinical field. Also, a depsipeptide compound is disclosed as an antitumor substance (European Patent Publication No. 352646).
Even at present, creation of antitumor agents having an unconventional chemical structure and novel skeleton is under examination.
On the other hand, TGF-β is first drawing attention as a factor which accelerates proliferation of cells and also accelerates transformation, it was now revealed that TGF-β acts as a factor which inhibits growth of various animal cells by the studies on its mechanism of actions (Cell, vol. 63, pp. 245–247, 1990). In addition, a large number of reports have been published regarding its relation to tumor cells (Br. Med. J., vol. 296, pp. 1621–1624, 1988; Br. J. Cancer, vol. 61, pp. 612–617, 1990; Br. J. Cancer, vol. 69, pp. 1006–1009, 1994; J. Cell Physiol., vol. 172, pp. 1–11, 1997; Growth Factors, vol. 7, pp. 207–213, 1992; J. Biol. Chem., vol. 272, pp. 3967–3972, 1997; Nature, vol. 360, pp. 361–364, 1992). Also, it has been reported that TGF-β receptor acts as a tumor suppressor gene in various tumors (International J. Hematology, vol. 65, pp. 97–104, 1997). In consequence, a compound-exhibiting TGF-β like activity has a possibility of becoming therapeutic agents for diseases related to said activity, such as an antitumor agent.